docs: def lint():
      """Run flake8 against all py files"""
      py_files = subprocess.check_output("git ls-files")
      if PY3:
          py_files = py_files.decode()
      py_files = [x for x in py_files.split() if x.endswith('.py')]
      py_files = ' '.join(py_files)
      sh("%s -m flake8 %s" % (PYTHON, py_files), nolog=True)